A series of Co(III) complexes, containing a tetradentate ligand and two water molecules in the first coordination sphere, are being investigated for use in the hydrolysis and sequencing of proteins. The complexes act from the N terminal end and cleave peptide bonds under mild conditions of pH and temperature. Activity relationships are being sought to gain the mildest conditions possible. BIBLIOGRAPHIC REFERENCES: Hill, H.A.O., Smith, B.E., Storm, C.B. and Ambler, R.P., The Proton Magnetic Resonance Spectra of a Co(II) Azurin, Biochem. Biophys. Res. Comm. 70, 783 (1976). Hill, H.A.O., Leer, J.P. Smith, B.E., Storm, C.B. and Ambler, R.P., A Possible Approach to the Investigation of the Structures of Copper Proteins: H.N.M.R. Spectra of Azurin, Biochem. Biophys. Res. Comm., 70, 331 (1976).